In a mobile communication system, a radio communication environment around a base station varies if a building is built near the base station or installation conditions of neighboring base stations of the base station are changed. Thus, it is a conventional practice to carry out a drive test in which an operator uses a measurement vehicle having measurement equipment on board to measure a radio environment and collect measurement data.
Such measurement and collection is helpful in network optimization (such as coverage optimization); however, it has a problem of requiring a large number of man-hours and high cost. To deal with this problem, the 3GPP (3rd Generation Partnership Project) as a standardization project for mobile communication systems is formulating a specification of MDT (Minimization of Drive Tests) for automating the measurement and collection by using a user terminal in Release 10 or later (refer to Non-patent Document 1, for example).
One mode of MDT is log-type MDT (referred to as “Logged MDT”). According to the current specification, Logged MDT is such a mode that a user terminal in IDLE mode measures a radio environment in accordance with measurement configuration information set by a network, logs as measurement data the measurement result together with location information and time information, and reports the measurement data to the network later.
Another mode of MDT is immediate-report-type MDT (referred to as “Immediate MDT”). According to the current specification, Immediate MDT is such a mode that a user terminal in CONNECTED mode measures a radio environment in accordance with measurement configuration information set by a network and immediately reports as measurement data the measurement result together with location information to the network.